The present invention relates to a reactor for preparing hydrogen cyanide (HCN) by the Andrussow process and to a process for preparing HCN which is performed using the inventive reactor.
The synthesis of hydrogen cyanide (HCN) by the Andrussow process is described in Ullmann's Encyclopedia of Industrial Chemistry, Volume 8, VCH Verlagsgesellschaft, Weinheim 1987, page 161-162. The reactant gas mixture, which generally comprises methane or a methane-containing natural gas stream, ammonia and oxygen, is passed through catalyst meshes in a reactor and converted at temperatures of approx. 1000° C. The oxygen needed is typically used in the form of air. the catalyst meshes consist generally of platinum or platinum alloys. The composition of the reactant gas mixture corresponds roughly to the stoichiometry of the exothermic net reaction equationCH4+NH3+3/2O2→HCN+3H2O dHr=−473.9 kJ.
The reaction gas flowing out comprises the HCN product, unconverted NH3 and CH4, and the essential by-products CO, H2, H2O, CO2 and a large proportion of N2.
The reaction gas is cooled rapidly in a waste heat boiler to approx. 150-200° C. and subsequently passes through a scrubbing column in which the unconverted NH3 is scrubbed out with dilute sulphuric acid and portions of the steam are condensed out. Also known is the absorption of NH3 with sodium hydrogenphosphate solution and subsequent recycling of the ammonia. In a downstream absorption column, HCN is absorbed in cold water and is prepared in a downstream rectification with a purity of greater than 99.5% by mass. The HCN-containing water obtained in the bottom of the column is cooled and recycled to the HCN absorption column.
A broad spectrum of possible embodiments of the Andrussow process is described in DE 549 055. Accordingly, reactors are also known for preparing HCN by the Andrussow process, one example of such a reactor being detailed in EP 1 001 843 B1. These reactors generally comprise an inlet for the reactants, an outlet for the products and a catalyst, which may be configured, for example, in the form of a plurality of platinum meshes arranged in succession. Immediately above the catalyst mesh, a gas-permeable protective layer may be provided, which serves as a heat shield and as a flashback guard.
The processes performed with known reactors already afford good yields with an acceptable energy demand. Owing to the significance of the product, however, there is a permanent effort to improve the performance and the effectiveness of the reactors.
In view of the prior art, it is thus an object of the present invention to provide a reactor which enables a particularly simple and inexpensive preparation of HCN. At the same time, the yield, the production output (kg of HCN/h) and the catalyst lifetime in particular should be increased. In addition, it was consequently an object of the present invention to provide a reactor which enables production of HCN with high HCN concentration in the reaction gas and hence particularly low energy demand in the HCN isolation.